Warriors: Omen of the Stars #4: Sign of the Moon by Erin Hunter
After the sharp-eyed jay and the roaring lion, peace will come on dove's gentle wing. The dark forces that have driven a rift between the four warrior Clans are growing stronger. While Lionblaze remains focused on maintaining an uneasy peace among the Clans, Jayfeather is summoned to the mountains by a desperate plea-the Tribe of Rushing Water has been plunged into disarray and stands on the brink of being lost forever.